Semiconductor integrated circuit apparatus and manufacturing method for same

ABSTRACT

A semiconductor integrated circuit apparatus and a manufacturing method for the same are provided in such a manner that a leak current caused by a ballast resistor is reduced, and at the same time, the inconsistency in the leak current is reduced. The peak impurity concentration of the ballast resistors is made smaller than the peak impurity concentration in the extension regions, and the depth of the ballast resistors is made greater than the depth of the extension regions.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of theprior Japanese Patent Application No. 2014-003914, filed on Jan. 14,2014, the entire contents of which are incorporated herein by reference.

FIELD

The present invention relates to a semiconductor integrated circuitapparatus and a manufacturing method for the same, and in particular, toa reduction of the leak current in transistors having a ballast resistoras well as a reduction in the inconsistency of the transistors.

BACKGROUND

The off-state voltage (BV_(sd)) of a high voltage (HV) drive transistoris determined by band-to-band tunneling (BTBT) that flows between thesubstrate beneath the gate and the drain. Accordingly, it is effectiveto form the junction for forming the drain region as gradual as possiblein order to increase the off-state voltage. Therefore, the tilt anglefor ion implantation for the formation of a lightly doped drain (LDD)region in a high voltage drive transistor is set to 45° so thatchanneling is generated and the LDD region is formed deep and with a lowconcentration.

Another idea for the conversion of Twist 45°, according to which theangle of direction of the ion implantation relative to the direction inwhich the gate electrode extends is set to 45°, has been proposed forthe pocket implantation of a low voltage drive transistor (see PatentDocuments 1: Japanese Unexamined Patent Publication 2010-129980 andPatent Documents 2: Domestic Re-publication of PCT InternationalPublication for Patent Application 2006-126245).

In addition, a transistor having a ballast resistor close to the drainregion is used as an electrostatic discharge (ESD) element used in theinput/output unit (I/O unit). This ballast resistor is gained togetherwith a salicide block, which is a mask for preventing the conversion tosilicide during the salicide process, and therefore, this process isdescribed in reference to FIG. 41.

FIG. 41 is a schematic cross-sectional diagram illustrating asemiconductor integrated circuit apparatus with a conventional ESDelement. This semiconductor integrated circuit apparatus is providedwith a high voltage drive transistor (HVTr), a low voltage drive I/Otransistor (LVI/OTr), and a low voltage drive transistor (LVTr).

The HVTr is provided with: a gate electrode 215, which is provided ontop of a p type well region 205 surrounded by an element isolationregion 202 provided in a silicon substrate 201 with a SiO₂ film 212 thatbecomes a gate insulating film in between; an n type LDD region 219; ann+type source region 226; and an n+type drain region 227.

The LVI/OTr is provided with: a gate electrode 216 that is provided ontop of a p type channel dope region 210 with a SiO₂ film 214 thatbecomes a gate insulating film in between, where the p type channel doperegion 210 is provided on the surface of the p type well region 207surrounded by an element isolation region 202 provided in the siliconsubstrate 201; an n type extension region 221; an n+type source region228; and an n+type drain region 229. In addition, an n type layer thatis simultaneously formed directly beneath the salicide block 225 duringthe process for forming the n type extension region 221 is provided as aballast resistor 232 so as to divide the n+type drain region 229.

The LVTr that forms an internal logic circuit is provided with: a gateelectrode 217 that is provided on top of a p type channel dope region211 with a SiO2 film 214 that becomes a gate insulating film in between,where the p type channel dope region 211 is provided on the surface of ap type well region 208 surrounded by an element isolation region 202provided in the silicon substrate 201; an n type extension region 222;an n+type source region 230; and an n+type drain region 231.

Next, a manufacturing process for a conventional semiconductorintegrated circuit apparatus with an ESD element is described inreference to FIGS. 42A to 42L. First, as illustrated in FIG. 42A, anelement isolation region 202 is formed in a silicon substrate 201 bymeans of shallow trench isolation (STI), and after that, a SiO₂ film 203with a thickness of 10 nm that becomes a sacrificial oxide film isformed on the surface. Next, the surface other than the region forforming a high voltage drive Tr is covered with a resist pattern 204 andion implanted with B so that a p type well region 205 of 1×10¹⁷ cm⁻³ to3×10¹⁷ cm⁻³, for example, is formed.

Next, as illustrated in FIG. 42B, the resist pattern 204 is removed, andafter that, a new resist pattern 206 is formed so as to cover the p typewell region 205. Then, B ions are implanted to form p type well regions207 and 208 of 8×10¹⁷ cm⁻³ to 12×10¹⁷ cm⁻³, for example.

Next, as illustrated in FIG. 42C, the resist pattern 206 is removed, andafter that, a new resist pattern 209 is formed so as to cover the p typewell region 205 and again ion implanted with B so that p type channeldope regions 210 and 211 are formed. Then, as illustrated in FIG. 42D,the resist pattern 209 is removed followed by the removal of the SiO₂film 203. After that, a SiO₂ film 212 with a thickness of 10 nm to 20nm, for example, which becomes a gate insulating film of a high voltagedrive Tr, is formed through thermal oxidation.

Next, as illustrated in FIG. 42E, a resist pattern 213 is formed so asto cover the p type well region 205, and after that, the SiO₂ film 212on the exposed p type well regions 207 and 208 is removed throughetching. After that, as illustrated in FIG. 42F, the resist pattern 213is removed, and then, thermal oxidation is carried out again so that aSiO₂ film 214 with a thickness of 1 nm to 3 nm, for example, whichbecomes a gate insulating film of a low voltage drive Tr, is formed onthe surface of the p type well regions 207 and 208.

Next, as illustrated in FIG. 42G, a polycrystalline silicon layer isdeposited on the p type well regions 205, 207, and 208 and then etchedso that gate electrodes 215 to 217 are formed. After that, asillustrated in FIG. 42H, a resist pattern 218 is formed so as to coverthe p type well regions 207 and 208. Then, this resist pattern 218 isused as a mask so that P ions are implanted in four directions at a tiltangle of 45° with an acceleration energy of 40 keV to 50 keV so that theamount of dosage becomes 5×10¹² cm⁻² to 10×10¹² cm⁻², and thus, an ntype LDD region 219 is formed in the p type well region 205.

Next, as illustrated in FIG. 42I, the resist pattern 218 is removed, andafter that, a new resist pattern 220 is formed so as to cover the p typewell region 205. This resist pattern 220 is used as a mask so that Bions are implanted in four directions at a tilt angle of 28° with anacceleration energy of 10 keV to 20 keV so that the amount of dosagebecomes 5×10¹² cm⁻² to 10×10¹² cm⁻², and thus, pocket regions (notshown) are formed. Subsequently, P ions are implanted in four directionsat a tilt angle of 0° with an acceleration energy of 1 keV to 2 keV sothat the amount of dosage becomes 3×10¹³ cm⁻² to 9×10¹³ cm⁻², and Asions are implanted in four directions at a tilt angle of 0° with anacceleration energy of 1 keV to 2 keV so that the amount of dosagebecomes 1×10¹⁴ cm⁻² to 2×10¹⁴ cm⁻², and thus, n type extension regions221 and 222 are formed in the p type well regions 207 and 208.

Next, as illustrated in FIG. 42J, the resist pattern 220 is removed, andafter that, a SiO₂ film is deposited on the entire surface, and then, aresist pattern 223 is formed so as to cover the region where a ballastresistor is to be formed and is subjected to anisotropic etching so thatside walls 224 are formed. At this time, the SiO₂ film that remainsunder the resist pattern 223 becomes a salicide block 225.

Next, as illustrated in FIG. 42K, the resist pattern 223 is removed, andafter that, P ions are implanted at a tilt angle of 0° with anacceleration energy of 5 keV to 10 keV so that the amount of dosagebecomes 1×10¹⁶ cm⁻² to 2×10¹⁶ cm⁻², and thus, n+type source regions 226,228, and 230 and n+type drain regions 227, 229, and 231 are formed. Atthis time, the n−type region directly beneath the salicide block 225becomes a ballast resistor 232.

Next, as illustrated in FIG. 42L, a Co film is deposited on the entiresurface, and after that, heat treatment is carried out so that a Cosilicide layer 233 is formed on the surfaces of the gate electrodes 215to 217, the n+type source regions 226, 228, and 230 as well as then+type drain regions 227, 229, and 231. Then, the unreacted Co film isremoved, and after that, heat treatment is again carried out so that theresistance of the Co silicide layer 233 is lowered. After that, thoughthe figures are not shown, an interlayer insulating film is formed, andthen, plugs that reach the Co silicide layer 233 are formed, and wiresconnected to these plugs are formed. The formation of such a wirestructure is repeated for the required number of layers. The transistoron the left is a high voltage drive transistor (HVTr), the transistor atthe center is a low voltage drive transistor with a ballast resistor(LVI/OTr), and the transistor on the right is a typical low voltagedrive transistor (LVTr).

SUMMARY

In a conventional semiconductor integrated circuit apparatus with a ESDelement, a leak current from the LVI/OTr that becomes the ESD elementbecomes a problem, and this state is described in reference to FIGS. 43Ato 45B. FIGS. 43A to 44 illustrate leak current characteristics of a lowvoltage drive transistor formed in a conventional semiconductorintegrated circuit apparatus with a transistor having a ballastresistor.

FIGS. 43A and 43B illustrate the results of the measurements of the leakcurrents of n channel type MOS transistors. FIG. 43A is a characteristicdiagram of a transistor having a ballast resistor, and FIG. 43B is acharacteristic diagram of a typical transistor. Here, the low voltagedrive transistors are ultra-high threshold NMOS transistors where thegate width W is 10 μm, the gate length L is 0.14 μm, and the drivevoltage is 1.2 V, and the results of the measurements are gained fromplots of 71 NMOS transistors. As illustrated in the figures, the leakcurrent characteristics of the typical transistors have a smallinconsistency, whereas the leak current characteristics of thetransistors having a ballast resistor have a large inconsistency.

FIG. 44 illustrates the median values of the leak currents from nchannel type MOS transistors and depicts the median values of theresults of the measurements in FIGS. 43A and 43B. As is clear from thefigure, the leak current from the transistors with a ballast resistor isgreater. This is considered to be because the leak current has increaseddue to the salicide block. In addition, it is possible for theinconsistency to increase due to the effects of the CoSi spike thatoccurs at the time of the formation of silicide electrodes.

Thus, the current distribution of each transistor is simulated, and theresults thereof are described in reference to FIGS. 45A and 45B. FIGS.45A and 45B illustrate the current distributions in the case where thegate voltage V_(G) is 0 V and the drain voltage V_(D) is 3 V. FIG. 45Ais a current distribution diagram of an LVTr, and FIG. 45B is a currentdistribution diagram of an LVI/OTr. Here, the solid lines in the figuresare equal current lines for demonstrating current distribution and thebroken lines depict the locations of pn junctions, and the single-dottedchain lines depict the locations of the depletion layers.

It can be seen from the comparison between FIG. 45A and FIG. 45B that aleak current that is greater than the junction leak current in theextension region of Tr flows under the salicide block in the case of anLVI/OTr. In addition, this junction leak current flows at the bottom ofthe salicide block instead of an end portion of the salicide block. Theextension region and the ballast resistor share the same impurityprofile, and therefore, it is possible for a leak current that isgreater than the junction leak current in the extension region of Tr toflow under the salicide block because the area of the ballast resistoris great and the location is close to the drain electrode to which 3 Vis applied.

One disclosed aspect provides a semiconductor integrated circuitapparatus, including a first insulated gate transistor that includes: asemiconductor substrate with at least a first well region of a firstconductivity type; a first gate electrode provided in the first wellregion of the first conductivity type with a first gate insulating filmin between; a first channel dope region of the first conductivity typeprovided directly beneath the first gate electrode; a first extensionregion of a second conductivity type that is a conductivity typeopposite the first conductivity type, a first source region of thesecond conductivity type, and a first drain region of the secondconductivity type provided on both sides of the first gate electrode;and a first ballast resistor of the second conductivity type thatseparates the first drain region, wherein the first insulated gatetransistor includes a second conductivity type channel, characterized inthat the peak impurity concentration of the first ballast resistor islower than the peak impurity concentration of the first extensionregion, and the depth of the first ballast resistor is greater than thedepth of the first extension region.

Another disclosed aspect provides a manufacturing method for asemiconductor integrated circuit apparatus, characterized by including:forming a number of element forming regions that are isolated from eachother by an element isolation region in a semiconductor substrate;introducing impurities of a first conductivity type into at least twoelement forming regions from among the element forming regions so as toform a first well region of the first conductivity type for forming alow voltage drive transistor and a second well region of the firstconductivity type for a high voltage drive transistor that is driven bya voltage higher than that of the transistor formed in the first wellregion of the first conductivity type; introducing impurities into thesemiconductor substrate in such a state that the second well region ofthe first conductivity type and a portion of the first well region ofthe first conductivity type are masked so as to form a first channeldope region of the first conductivity type on the surface of anotherportion of the first well region of the first conductivity type; forminga first gate electrode in the first channel dope region with a firstgate insulating film in between, and at the same time forming a secondgate electrode in the second well region of the first conductivity typewith a second gate insulating film in between; introducing impuritiesinto the second well region of the first conductivity type using thesecond gate electrode as a mask so as to form a low concentrationsource/drain region of a second conductivity type that is a conductivitytype opposite the first conductivity type, and at the same time maskingthe first channel dope region in the first well region of the firstconductivity type so as to form a first resistor forming layer of thesecond conductivity type; introducing impurities into the first channeldope region using the first gate electrode as a mask so as to form afirst extension region of the second conductivity type; and introducingimpurities into the first well region of the first conductivity type andthe second well region of the first conductivity type using side wallsof the first gate electrode and the second gate electrode as well as aninsulating film pattern selectively provided on the first resistorforming layer as a mask so as to form a first source region and a firstdrain region of the second conductivity type of which the concentrationis higher than that in the low concentration source/drain region as wellas a second source region and a second drain region of the secondconductivity type, of which the concentration is higher than that of thelow concentration source/drain region, respectively, and thus convertingthe first resistor forming layer directly beneath the insulating filmpattern to a first ballast resistor.

Still another disclosed aspect provides a manufacturing method for asemiconductor integrated circuit apparatus including: forming a numberof element forming regions isolated from each other by an elementisolation region in a semiconductor substrate; introducing impurities ofa first conductivity type into at least one element forming region fromamong the element forming regions so as to form a first well region ofthe first conductivity type; introducing impurities of a secondconductivity type into at least one element forming region from amongthe other element forming regions so as to form a first well region ofthe second conductivity type; forming a first channel dope region of thefirst conductivity type in a portion of the first well region of thefirst conductivity type, and at the same time forming a first resistorforming layer of the first conductivity type in a portion of the firstwell region of the second conductivity type; forming a second resistorforming layer of the second conductivity type in a region of the firstwell region of the first conductivity type other than the first channeldope region, and at the same time forming a second channel dope regionof the second conductivity type in a region of the first well region ofthe second conductivity type other than the first resistor formingregion; providing a first gate electrode in the first well region of thefirst conductivity type with a first gate insulating film in between;providing a second gate electrode in the first well region of the secondconductivity type with a second gate insulating film in between;introducing impurities into the first well region of the firstconductivity type using first side walls on the first gate electrode andthe first insulating film pattern provided on the second resistorforming layer as a mask so as to form a first source region and a firstdrain region of the second conductivity type, of which the impurityconcentration is higher than that of the second resistor forming layer,and at the same time to convert the second resistor forming layerdirectly beneath the first insulating film pattern to a second ballastresistor; introducing impurities into the first well region of thesecond conductivity type using the second side walls provided on thesecond gate electrode and the second insulating film pattern provided onthe first resistor forming layer as a mask so as to form a second sourceregion and a second drain region of the first conductivity type, ofwhich the impurity concentration is higher than that of the firstresistor forming layer, and at the same time to convert the firstresistor forming layer directly beneath the second insulating filmpattern to a first ballast resistor.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional diagram illustrating thesemiconductor integrated circuit apparatus with an insulated gatetransistor having a ballast resistor according to an embodiment of thepresent invention;

FIGS. 2A and 2B are a diagram and a graph illustrating the distributionof the impurity concentration directly beneath the ballast resistor inthe n channel insulated gate transistor having a ballast resistoraccording to an embodiment of the present invention;

FIGS. 3A and 3B are a diagram and a graph illustrating the distributionof the impurity concentration directly beneath the ballast resistor inthe p channel insulated gate transistor having a ballast resistoraccording to an embodiment of the present invention;

FIGS. 4A and 4B are diagrams illustrating the effects of the channeldope region in the step of forming an n type ballast resistor;

FIGS. 5A and 5B are diagrams illustrating the effects of the channeldope region in the step of forming a p type ballast resistor;

FIGS. 6A and 6B are graphs illustrating the inconsistency in the sheetresistance in the case where the through-oxide film is 0 nm during theprocess of forming a ballast resistor;

FIG. 7 is a diagram illustrating channeling during the step of ionimplantation;

FIGS. 8A and 8B are diagrams illustrating a second mode of the step offorming a ballast resistor;

FIGS. 9A and 9B are graphs illustrating the dependency of theinconsistency in the sheet resistance due to a tilt angle on thethickness of the through oxide film;

FIGS. 10A and 10B are graphs illustrating the dependency of the sheetresistance on the thickness of the through-oxide film in the case wherethe tilt angle is 45°±1°;

FIGS. 11A and 11B are graphs illustrating the dependency of the sheetresistance on the thickness of the through oxide film in the case wherethe tilt angle is 45°±0.5°;

FIG. 12 is a diagram illustrating the effects of side etching at thetime of through-oxide film patterning;

FIG. 13 is a diagram illustrating a third mode of the step of forming aballast resistor;

FIG. 14 is a graph illustrating the dependency of the threshold voltageon the tilt angle in the case where no deposited through-oxide film isprovided;

FIGS. 15A and 15B are graphs illustrating the dependency of thedeviation ΔVth in the threshold voltage on the thickness of thedeposited through-oxide film;

FIGS. 16A and 16B are diagrams for illustrating a step in the middle ofthe manufacturing process for a semiconductor integrated circuitapparatus according to the first embodiment of the present invention;

FIGS. 16C and 16D are diagrams for illustrating a step after the step inFIG. 16B of the manufacturing process for a semiconductor integratedcircuit apparatus according to the first embodiment of the presentinvention;

FIGS. 16E and 16F are diagrams for illustrating a step after the step inFIG. 16D of the manufacturing process for a semiconductor integratedcircuit apparatus according to the first embodiment of the presentinvention;

FIGS. 16G and 16H are diagrams for illustrating a step after the step inFIG. 16F of the manufacturing process for a semiconductor integratedcircuit apparatus according to the first embodiment of the presentinvention;

FIGS. 16I and 16J are diagrams for illustrating a step after the step inFIG. 16H of the manufacturing process for a semiconductor integratedcircuit apparatus according to the first embodiment of the presentinvention;

FIGS. 17A and 17B are graphs illustrating the results of themeasurements of a leak current of an n channel type MOS transistor;

FIG. 18 is a graph illustrating the median values of the leak currentsfrom n channel type MOS transistors;

FIGS. 19A and 19B are diagrams illustrating the results of simulation ofthe distribution of the impurity concentration in the n channel type lowvoltage drive transistor with a ballast resistor according to the firstembodiment of the present invention;

FIG. 20 is a graph illustrating the distribution of the effectiveimpurity concentration;

FIGS. 21A and 21B are graphs illustrating the results of themeasurements of a leak current from a p channel type MOS transistor;

FIG. 22 is a graph illustrating the median value of the leak currentfrom a p channel type MOS transistor;

FIGS. 23A and 23B are diagrams illustrating the results of simulation ofthe distribution of the impurity concentration in the p channel type lowvoltage drive transistor with a ballast resistor according to the firstembodiment of the present invention;

FIG. 24 is a graph illustrating the distribution of the effectiveimpurity concentration;

FIG. 25 is a schematic cross-sectional diagram illustrating thesemiconductor integrated circuit apparatus according to the secondembodiment of the present invention;

FIGS. 26A and 26B are diagrams for illustrating a flash memory unit in astep in the middle of the manufacturing process for a semiconductorintegrated circuit apparatus according to the second embodiment of thepresent invention;

FIGS. 26C and 26D are diagrams for illustrating the flash memory unit ina step after the step in FIG. 26B of the manufacturing process for asemiconductor integrated circuit apparatus according to the secondembodiment of the present invention;

FIGS. 26E and 26F are diagrams for illustrating the flash memory unit ina step after the step in FIG. 26D of the manufacturing process for asemiconductor integrated circuit apparatus according to the secondembodiment of the present invention;

FIGS. 26G and 26H are diagrams for illustrating the flash memory unit ina step after the step in FIG. 26F of the manufacturing process for asemiconductor integrated circuit apparatus according to the secondembodiment of the present invention;

FIGS. 26I and 26J is a diagram for illustrating the flash memory unit ina step after the step in FIG. 26H of the manufacturing process for asemiconductor integrated circuit apparatus according to the secondembodiment of the present invention;

FIGS. 27A and 27B are diagrams for illustrating a step in the middle ofthe manufacturing process for a semiconductor integrated circuitapparatus according to the third embodiment of the present invention;

FIGS. 27C and 27D are diagrams for illustrating a step after the step inFIG. 27B of the manufacturing process for a semiconductor integratedcircuit apparatus according to the third embodiment of the presentinvention;

FIGS. 27E and 27F are diagrams for illustrating a step after the step inFIG. 27D of the manufacturing process for a semiconductor integratedcircuit apparatus according to the third embodiment of the presentinvention;

FIGS. 27G and 27H are diagrams for illustrating a step after the step inFIG. 27F of the manufacturing process for a semiconductor integratedcircuit apparatus according to the third embodiment of the presentinvention;

FIGS. 27I and 27J is a diagram for illustrating a step after the step inFIG. 27H of the manufacturing process for a semiconductor integratedcircuit apparatus according to the third embodiment of the presentinvention;

FIGS. 28A and 28B illustrate profiles of the impurity concentrations inthe ballast resistor portion of an NMOS;

FIGS. 29A and 29B illustrate profiles of the impurity concentrations inthe ballast resistor portion of a PMOS;

FIGS. 30A and 30B are diagrams for illustrating a step in the middle ofthe manufacturing process for a semiconductor integrated circuitapparatus according to the fourth embodiment of the present invention;

FIGS. 30C and 30D are diagrams for illustrating a step after the step inFIG. 30B of the manufacturing process for a semiconductor integratedcircuit apparatus according to the fourth embodiment of the presentinvention;

FIGS. 30E and 30F are diagrams for illustrating a step after the step inFIG. 30D of the manufacturing process for a semiconductor integratedcircuit apparatus according to the fourth embodiment of the presentinvention;

FIGS. 30G and 30H are diagrams for illustrating a step after the step inFIG. 30F of the manufacturing process for a semiconductor integratedcircuit apparatus according to the fourth embodiment of the presentinvention;

FIGS. 30I and 30J are diagrams for illustrating a step after the step inFIG. 30H of the manufacturing process for a semiconductor integratedcircuit apparatus according to the fourth embodiment of the presentinvention;

FIGS. 31A and 31B are diagrams for illustrating a step in the middle ofthe manufacturing process for a complementary type semiconductorintegrated circuit apparatus according to the fifth embodiment of thepresent invention;

FIGS. 31C and 31D are diagrams for illustrating a step after the step inFIG. 31B of the manufacturing process for a complementary typesemiconductor integrated circuit apparatus according to the fifthembodiment of the present invention;

FIGS. 31E and 31F are diagrams for illustrating a step after the step inFIG. 31D of the manufacturing process for a complementary typesemiconductor integrated circuit apparatus according to the fifthembodiment of the present invention;

FIGS. 31G and 31H are diagrams for illustrating a step after the step inFIG. 31F of the manufacturing process for a complementary typesemiconductor integrated circuit apparatus according to the fifthembodiment of the present invention;

FIGS. 31I and 31J are diagrams for illustrating a step after the step inFIG. 31H of the manufacturing process for a complementary typesemiconductor integrated circuit apparatus according to the fifthembodiment of the present invention;

FIGS. 31K and 31L are diagrams for illustrating a step after the step inFIG. 31J of the manufacturing process for a complementary typesemiconductor integrated circuit apparatus according to the fifthembodiment of the present invention;

FIGS. 32A to 32C are diagrams illustrating the dependency of thedistribution of the impurity concentration in an n type ballast resistorregion;

FIGS. 33A to 33C are diagrams illustrating the dependency of thedistribution of the impurity concentration in a p type ballast resistorregion on the amount of channel dosage;

FIGS. 34A and 34B are graphs illustrating the results of evaluation ofthe leak current in ballast resistor regions;

FIGS. 35A and 35B are diagrams illustrating the results of simulation ofthe distribution of the impurity concentration in an n channel type lowvoltage drive transistor with a ballast resistor according to the fifthembodiment of the present invention;

FIG. 36 is a graph showing the distribution of the effective impurityconcentration;

FIGS. 37A and 37B are diagrams illustrating the results of simulation ofthe distribution of the impurity concentration in a p channel type lowvoltage drive transistor with a ballast resistor according to the fifthembodiment of the present invention;

FIG. 38 is a graph showing the distribution of the effective impurityconcentration;

FIGS. 39A and 39B are graphs illustrating the selectivity of the sheetresistance in an n channel type MOS transistor;

FIGS. 40A and 40B are graphs illustrating the sheet resistanceselectivity in a p channel type MOS transistor;

FIG. 41 is a schematic cross-sectional diagram illustrating aconventional semiconductor integrated circuit apparatus with an ESDelement;

FIGS. 42A and 42B are diagrams for illustrating a step in the middle ofthe manufacturing process for a conventional semiconductor integratedcircuit apparatus with a ESD element;

FIGS. 42C and 42D are diagrams for illustrating a step after the step inFIG. 42B of the manufacturing process for a conventional semiconductorintegrated circuit apparatus with an ESD element;

FIGS. 42E and 42F are diagrams for illustrating a step after the step inFIG. 42D of the manufacturing process for a conventional semiconductorintegrated circuit apparatus with an ESD element;

FIGS. 42G and 42H are diagrams for illustrating a step after the step inFIG. 42F of the manufacturing process for a conventional semiconductorintegrated circuit apparatus with an ESD element;

FIGS. 42I and 42J are diagrams for illustrating a step after the step inFIG. 42H of the manufacturing process for a conventional semiconductorintegrated circuit apparatus with an ESD element;

FIGS. 42K and 42L are diagrams for illustrating a step after the step inFIG. 42J of the manufacturing process for a conventional semiconductorintegrated circuit apparatus with an ESD element;

FIGS. 43A and 43B illustrate the results of the measurements of the leakcurrents of n channel type MOS transistors;

FIG. 44 illustrates the median values of the leak currents from nchannel type MOS transistors;

FIGS. 45A and 45B illustrate the current distributions in the case wherethe gate voltage VG is 0 V and the drain voltage VD is 3 V.

DESCRIPTION OF EMBODIMENTS

Here, the semiconductor integrated circuit apparatus with an insulatedgate transistor having a ballast resistor according to embodiments ofthe present invention is described in reference to FIGS. 1 to 15. FIG. 1is a schematic cross-sectional diagram illustrating the semiconductorintegrated circuit apparatus with an insulated gate transistor having aballast resistor according to an embodiment of the present invention.The semiconductor integrated circuit apparatus is provided with a firstinsulated gate transistor 1 having a ballast resistor and a secondinsulated gate transistor 2 that is driven by a voltage higher than thatof the first insulated gate transistor 1.

The second insulated gate transistor 2 is provided in a first wellregion 12 of a first conductivity type that is surrounded by an elementisolation region 11 formed in a semiconductor substrate 10. A gateinsulating film 13 and a gate electrode 14 are provided on the surfaceof a first well region 12 together with side walls 15, LDD regions 16 ofa second conductivity type that is a conductivity type opposite thefirst conductivity type, and a source region 17 and a drain region 18 ofthe second conductivity type on the two sides of the gate electrode 14.

The first insulated gate transistor 1 is provided in a second wellregion 21 of the first conductivity type surrounded by the elementisolation region 11 formed in the semiconductor substrate 10. A channeldope region 22 is provided in the vicinity of the surface of the secondwell region 21, and a gate insulating film 23 and a gate electrode 24are provided on top of the surface. Side walls 25 are provided on thetwo sides of the gate electrode 24 together with extension regions 26 onthe second conductivity type as well as a source region 27 and a drainregion 28 of the second conductivity type. In addition, a ballastresistor unit 30 is provided in the drain region 28. This ballastresistor unit 30 is provided with a resistor layer 32 of the secondconductivity type directly beneath the insulating film pattern 31 thatbecomes a salicide block. This resistor layer 32 is formed in the stepof forming the LDD regions 16 of the second insulated gate transistor 2,and therefore effectively has the same depth and the same impurityconcentration of the second conductivity type as the LDD regions 16.

In addition, a third well region 41 of the first conductivity typesurrounded by the element isolation region may be formed in thesemiconductor substrate 10 so that a third insulated gate transistor 3that is driven by a voltage lower than that of the second insulated gatetransistor can be provided in the third well region 41. The thirdinsulated gate transistor 3 is formed during the manufacturing processfor the first insulated gate transistor 1, and thus is formed in thesame steps, excluding the steps of forming a ballast resistor unit 30 inthe first insulated gate transistor 1.

FIGS. 2A and 2B are a diagram and a graph illustrating the distributionof the impurity concentration directly beneath the ballast resistor inthe n channel insulated gate transistor having a ballast resistoraccording to an embodiment of the present invention. FIG. 2A is adistribution diagram along a cross-section, and FIG. 2B illustrates aprofile of the effective impurity concentration in the ballast resistorunit. FIG. 2B also illustrates a profile of the effective impurityconcentration in the ballast resistor unit in the conventional LVI/OTrin FIG. 41. As is clearly seen from FIG. 2A, the distribution of theimpurity concentration in the mode of the present invention is gradual.As is also clearly seen from the comparison with the conventionalLVI/OTr in FIG. 2B, the location of the pn junction is deeper and thepeak impurity concentration is greatly lower in the mode of the presentinvention. Here, the n type region is depicted by the grainy area andthe p type region is depicted by the white area, and the same depictionsare used in the following diagram illustrating the distribution of theimpurity concentrations.

FIGS. 3A and 3B are a diagram and a graph illustrating the distributionof the impurity concentration directly beneath the ballast resistor inthe p channel insulated gate transistor having a ballast resistoraccording to an embodiment of the present invention. FIG. 3A is adistribution diagram along a cross-section, and FIG. 3B illustrates aprofile of the effective impurity concentration in the ballast resistorunit. As is clearly seen from FIG. 3A in this case as well, thedistribution of the impurity concentration in the mode of the presentinvention is gradual. As is also clearly seen from the comparison withthe conventional LVI/OTr in FIG. 3B, the location of the pn junction isdeeper and the peak impurity concentration is greatly lower in the modeof the present invention.

FIGS. 4A and 4B are diagrams illustrating the effects of the channeldope region in the step of forming an n type ballast resistor. FIG. 4Ais a diagram illustrating for the purpose of comparison the distributionof the impurity concentration along a cross-section in the vicinity ofthe ballast resistor in the case where a channel dope region is providedin the ballast resistor forming region. FIG. 4B is a diagramillustrating the distribution of the impurity concentration along across-section in the vicinity of the ballast resistor according to themode of the present invention. As illustrated in FIG. 4A, in the casewhere a channel dope region is provided, the n type layer for formingthe ballast resistor is divided instead of being formed in the surfaceportion. Meanwhile, as can be seen from FIG. 4B, an excellent n typelayer is formed in the case where a channel dope region is not formed.

FIGS. 5A and 5B are diagrams illustrating the effects of the channeldope region in the step of forming a p type ballast resistor. FIG. 5A isa diagram illustrating for the purpose of comparison the distribution ofthe impurity concentration along a cross-section in the vicinity of theballast resistor in the case where a channel dope region is provided inthe ballast resistor forming region. FIG. 5B is a diagram illustratingthe distribution of the impurity concentration along a cross-section inthe vicinity of the ballast resistor according to the mode of thepresent invention. As illustrated in FIG. 5A, in the case where achannel dope region is provided, the p type layer for forming theballast resistor is divided instead of being formed in the surfaceportion. Meanwhile, as can be seen from FIG. 5B, an excellent p typelayer is formed in the case where a channel dope region is not formed.

Next, the effects of a through-oxide film during the step of forming aballast resistor are examined in reference to FIGS. 6A, 6B, and 7. FIGS.6A and 6B are graphs illustrating the inconsistency in the sheetresistance in the case where the through-oxide film is 0 nm during theprocess of forming a ballast resistor. FIG. 6A is a graph illustratingthe inconsistency in the sheet resistance of an NMOS, and FIG. 6B is agraph illustrating the inconsistency in the sheet resistance of a PMOS.Here, the characteristics of transistors (UHVt) with an ultra-highthreshold voltage that are driven by a low voltage are illustrated. Asis clear from the figures, the channeling factor becomes great and theinconsistency in the sheet resistance due to the tilt angle becomessignificant in the case where no through-oxide films are provided inboth cases of an NMOS and a PMOS.

FIG. 7 is a diagram illustrating channeling during the step of ionimplantation, where a 45° substrate is illustrated, on which elementsare formed in the direction <100>, which is the direction rotated by 45°relative to a notch or an orientation flat that is the standard of thecrystal orientation provided in the wafer. The line of 0° in the figuredenotes the direction of the crystal surface as viewed from thedirection of 0° relative to the standard line of the 45° substrate, andthe lateral axis denotes a tilt angle. Meanwhile, 45° denotes thedirection of the crystal surface as viewed from the direction rotated by45° relative to the standard line of the 45° substrate. Here, thedirection <100> denotes the direction that is equivalent to thedirection [100], and the direction [100] means the directionperpendicular to the surface (100).

In the step of forming the LDDs of a high voltage drive transistor, suchconditions that allow channeling to occur are selected becauseimpurities are implanted relatively deeply. Accordingly, in the casewhere the rotation angle is 0°, channeling occurs by adjusting the tiltangle to 45° so that the direction <011> is brought about. In the casewhere ions are implanted in the direction rotated by 45°, the direction<112> is brought about by adjusting the tilt angle to 35°.

Thus, LDD regions are formed under the conditions where channelingoccurs, but the LDD forming regions have a SiO₂ film that becomes a gateinsulating film as a through-oxide film, and therefore, the dispersionin the sheet resistance is low. Meanwhile, the thin SiO₂ film thatbecomes a gate insulating film is removed from the ballast resistorforming region in the step of etching for the formation of a gateelectrode, and the through oxide film becomes essentially 0 nm.Accordingly, as illustrated in FIGS. 6A and 6B, the inconsistency in thesheet resistance due to the tilt angle becomes very great.

Taking the above into consideration, a second mode of the step offorming a ballast resistor is described in reference to FIGS. 8A and 8B.FIGS. 8A and 8B are diagrams illustrating a second mode of the step offorming a ballast resistor. FIG. 8A is a cross-sectional diagram in thecase where the through-oxide film is 0 nm, and FIG. 8B is across-sectional diagram in the case where a through-oxide film isprovided. In the second mode, a through-oxide film 35 is formed in theballast resistor forming region, and therefore, the inconsistency in thesheet resistance due to a tilt angle can be reduced. In this case, theSiO₂ film that remains in the ballast resistor forming region andbecomes a gate oxide film of a high voltage drive transistor is used asa through-oxide film.

FIGS. 9A and 9B are graphs illustrating the dependency of theinconsistency in the sheet resistance due to a tilt angle on thethickness of the through oxide film. FIG. 9A is a graph illustrating thedependency of the inconsistency in the sheet resistance due to a tiltangle in an NMOS on the thickness of the through oxide film, and FIG. 9Bis a graph illustrating the dependency of the inconsistency in the sheetresistance due to a tilt angle in an PMOS on the thickness of thethrough oxide film. Here, the conditions for ion implantation in thestep of forming the LDDs in an HVTr are used. As can be clearly seenfrom the figures, the inconsistency is small when the film thickness ofthe through oxide film is 3 nm or greater in either case. Accordingly,it is desirable for the film thickness to be 3 nm or greater in the casewhere a through-oxide film is provided.

FIGS. 10A and 10B are graphs illustrating the dependency of the sheetresistance on the thickness of the through-oxide film in the case wherethe tilt angle is 45°±1°. FIG. 10A is a graph illustrating thedependency of the sheet resistance on the thickness of the through-oxidefilm in an NMOS, and FIG. 10B is a graph illustrating the dependency ofthe sheet resistance on the thickness of the through-oxide film in aPMOS. Here, the ion implantation conditions in the step of forming theLDDs in an HVTr are again used. In this case as well, as can be clearlyseen from the figures, the inconsistency in the resistance can be madesmall in the case where the film thickness of the through-oxide film is3 nm or greater.

FIGS. 11A and 11B are graphs illustrating the dependency of the sheetresistance on the thickness of the through oxide film in the case wherethe tilt angle is 45°±0.5°. FIG. 11A is a graph illustrating thedependency of the sheet resistance on the thickness of the through-oxidefilm in an NMOS, and FIG. 11B is a graph illustrating the dependency ofthe sheet resistance on the thickness of the through-oxide film in aPMOS. Here, the ion implantation conditions in the step of forming theLDDs in an HVTr are again used. In this case as well, as can be clearlyseen from the figures, the inconsistency in the resistance can be madesmall in the case where the film thickness of the through-oxide film is3 nm or greater.

In the case where the same oxide film as the gate oxide film of the HVTris used as a through-oxide film as in the second mode, the impurityconcentration and the depth of the ballast resistor are essentiallyequal to the impurity concentration and the depth of the LDD regions ofthe HVTr.

Next, the effects of side etching at the time of through-oxide filmpatterning in the second mode are described in reference to FIG. 12.FIG. 12 is a diagram illustrating the effects of side etching at thetime of through-oxide film patterning. A SiO₂ film that becomes a gateinsulating film of an HVTr is formed in a first well region 21 of thefirst conductivity type and is etched using the resist pattern 36 as amask so as to be kept as a through-oxide film 35. At this time, theetchant having HF permeates the through-oxide film 35 from the sideportion directly beneath the resist pattern 36 so that a side etchedportion 37 is created, and there is a risk that the side etched portion37 may reach the region in which a salicide block is to be formed.

As a result, there is a risk that a region having no through-oxide filmmay be created at the time of ion implantation for forming a layer ofthe second conductivity type that becomes a ballast resistor, and thereis a concern that the inconsistency in the ballast resistance mayincrease, and thus, it is possible to form a through-oxide film of adeposited oxide film so that no side etched portion is created.

FIG. 13 is a diagram illustrating a third mode of the step of forming aballast resistor where a through-oxide film is formed as a depositedthrough-oxide film 38, and after that, the resist pattern 33 is used asa mask to implant impurities 34 of the second conductivity type. Thedeposited through-oxide film 38 may be formed after the formation of theextension regions 26 of the second conductivity type.

FIG. 14 is a graph illustrating the dependency of the threshold voltageon the tilt angle in the case where no deposited through-oxide film isprovided. Here, the characteristics of a low threshold voltagetransistor (LVthTr) and a standard threshold voltage transistor(SVthTr), of which the gate width W is 10 μm and the gate length is 0.7μm, are examined. Approximately the same characteristics are gained inthe cases of tilt angle 45°/rotation angle 0° and tilt angle35°/rotation angle 45° when channeling occurs, while the tendency of thethreshold voltage Vth to increase is observed in the case of tilt angle28°/rotation angle 0° when it is difficult for channeling to occur.

FIGS. 15A and 15B are graphs illustrating the dependency of thedeviation ΔVth in the threshold voltage on the thickness of thedeposited through-oxide film, and the deviation of the threshold voltageVth in the case where a deposited through-oxide film is provided fromthe threshold voltage Vth in the case where no deposited through oxidefilm is provided, as in FIG. 14, is illustrated. FIG. 15A illustratesthe dependency of the deviation ΔVth in the threshold voltage of an NMOSon the thickness of the deposited through-oxide film, and FIG. 15Billustrates the dependency of the deviation ΔVth in the thresholdvoltage of a PMOS on the thickness of the deposited through-oxide film.Provided that the tolerance range of the deviation ΔVth in the thresholdvoltage is within 30 mV, the deviation ΔVth in the threshold voltage ofan NMOS is within the tolerance range under any implantation conditionsas long as the film thickness of the deposited through-oxide film is 11nm or less.

Meanwhile, in the case of a PMOS, it is necessary for the film thicknessto be 7 nm or less under the conditions of tilt angle 45°/rotation angle0°, and it is necessary for the film thickness to be 11 nm or less inthe case of tilt angle 35°/rotation angle 45°. Though ΔVth is smaller inthe case of tilt angle 28°/rotation angle 0°, the withstand voltagecannot be secured as part of the element characteristics.

In the case where a deposited oxide film is provided as a through-oxidefilm as in the third mode, the impurity concentration and the depth ofthe ballast resistor are approximately equal to the impurityconcentration and the depth of the LDD regions in an HVTr and depend onthe film thickness.

In the case of a CMOS, ballast resistors may be formed in well regions,of which the conductivity types are opposite each other, in the steps offorming channel dope regions of different conductivity types. In thiscase, the impurity concentration of a ballast resistor has the samevalue that is gained by subtracting the value of the impurityconcentration of the well region containing the ballast resistor fromthe value of the impurity concentration of the channel dope regionformed in the well region of the opposite conductivity type. Inaddition, the depth of the ballast resistor becomes the same as thedepth of the channel dope region formed in the well region of theopposite conductivity type.

According to the disclosed semiconductor integrated circuit apparatusand manufacturing method for the same, it is possible to reduce a leakcurrent caused by a ballast resistor and to reduce the inconsistency inthe leak current.

First Embodiment

Next, the semiconductor integrated circuit apparatus according to thefirst embodiment of the present invention is described in reference toFIGS. 16A to 24. First, the manufacturing process for the semiconductorintegrated circuit apparatus according to the first embodiment of thepresent invention is described in reference to FIGS. 16A to 16J. Asillustrated in FIG. 16A, an element isolation region 52 is formed in asilicon substrate 51 by means of shallow trench isolation (STI), andafter that, a SiO₂ film 53, of which the thickness is 10 nm, forexample, and which becomes a sacrificial oxide film, is formed on thesurface. Then, the silicon substrate 51 is covered with a resist pattern54, excluding the high voltage drive Tr forming region, and is ionimplanted with B so that a p type well region 55 of 2.2×10¹⁷ cm⁻³, forexample, is formed.

Next, as illustrated in FIG. 16B, the resist pattern 54 is removed, andthen, a new resist pattern 56 is formed so as to cover the p type wellregion 55. After that, B ions are implanted so as to form p type wellregions 57 and 58 of 9.6×10¹⁷ cm⁻³, for example.

Next, as illustrated in FIG. 16C, the resist pattern 56 is removed, andthen, a new resist pattern 59 is formed so as to cover the p type wellregion 55 and a portion of the p type well region 57, and B ions areagain implanted so as to form p type channel dope regions 60 and 61.Next, as illustrated in FIG. 16D, the resist pattern 59 is removed, andthen, the SiO₂ film 53 is removed. After that, a SiO₂ film 62, of whichthe thickness is 16 nm, for example, and which becomes the gateinsulating film of a high voltage drive Tr, is formed through thermaloxidation.

Next, as illustrated in FIG. 16E, a resist pattern 63 is formed so as tocover the p type well region 55, and then, the SiO₂ film 62 on theexposed p type well regions 57 and 58 is removed through etching. Afterthat, as illustrated in FIG. 16F, the resist pattern 63 is removed, andthen, thermal oxidation is again carried out so that a SiO₂ film 64, ofwhich the thickness is 1.8 nm and which becomes the gate insulating filmof a low voltage drive Tr, is formed on the surface of the p type wellregions 57 and 58.

Next, as illustrated in FIG. 16G, a polycrystalline silicon layer isdeposited on the p type well regions 55, 57, and 58, and then is etchedso as to form gate electrodes 65 to 67. In this etching step, the thinSiO₂ film 64 that has been exposed essentially disappears. After that, aresist pattern 68 is formed so as to cover the region in the p type wellregion 57 where the p type channel dope region 60 is formed as well asthe p type well region 58. Then, the resist pattern 68 is used as a maskwhen P ions are implanted in four directions at a tilt angle of 45° withan acceleration energy of 46 keV, for example, so that the amount ofdosage becomes 8.0×10¹² cm⁻², for example, and thus, an n type LDDregion 69 is formed in the p type well region 55, and at the same time,n−type region 70 is formed in the exposed portion of the p type wellregion 57.

Next, as illustrated in FIG. 16H, the resist pattern 68 is removed, andthen, a new resist pattern 71 is formed so as to cover the p type wellregion 55 and the n−type region 70. This resist pattern 71 is used as amask when B ions are implanted in four directions at a tilt angle of 28°with an acceleration energy of 15 keV, for example, so that the amountof dosage becomes 7.4×10¹² cm⁻², and thus, pocket regions (not shown)are formed. Subsequently, P ions are implanted in four directions at atilt angle of 0° with an acceleration energy of 1 keV, for example, sothat the amount of dosage becomes 6.0×10¹³ cm⁻², for example, and Asions are implanted in four directions at a tilt angle of 0° with anacceleration energy of 1 keV, for example, so that the amount of dosagebecomes 1.0×10¹⁴ cm⁻², for example, and thus, n type extension regions72 and 73 are formed in the p type well regions 57 and 58.

Next, as illustrated in FIG. 16I, the resist pattern 71 is removed, andthen, a SiO₂ film is deposited on the entire surface, a resist pattern(not shown) is formed so as to cover the ballast resistor formingregion, and anisotropic etching is carried out so as to form side walls75. At this time, the SiO₂ film that remains beneath the resist patternbecomes a salicide block 76.

Next, the resist pattern is removed, and then, P ions are implanted infour directions at a tilt angle of 0° with an acceleration energy of 8keV, for example, so that the amount of dosage becomes 1.2×10¹⁶ cm⁻²,for example, and thus, n+type source regions 77, 79, and 81 as well asn+plus type drain regions 78, 80, and 82 are formed. At this time, then−type region directly beneath the salicide block 76 becomes a ballastresistor 83.

Next, as illustrated in FIG. 16J, a Co film is deposited on the entiresurface, and then, heat treatment is carried out so that Co silicidelayers 84 are formed on the surface of the gate electrodes 65 to 67, then+type source regions 77, 79, and 81 as well as the n+type drain regions78, 80, and 82. Then, the unreacted portions of the Co film are removed,and then, heat treatment is again carried out so as to lower theresistance of the Co silicide layers 84. After that, though not shown,an interlayer insulating film is formed, and then, plugs are formed soas to reach the Co silicide layers 84, and wires connected to theseplugs are formed. The formation of such a wire structure is repeated forthe required number of layers, and as a result, the basic structure ofthe semiconductor integrated circuit apparatus according to the firstembodiment of the present invention is complete. The transistor on theleft side is a high voltage drive transistor (HVTr), the transistor atthe center is a low voltage drive transistor with a ballast resistor(LVI/OTr), and the transistor on the right side is a typical low voltagedrive transistor (LVTr).

FIGS. 17A, 17B, and 18 are graphs illustrating the characteristics ofthe low voltage drive transistor according to the first embodiment ofthe present invention. FIGS. 17A and 17B are graphs illustrating theresults of the measurements of a leak current of an n channel type MOStransistor. FIG. 17A is a characteristic graph for a typical transistorto be compared, and FIG. 17B is a characteristic graph of the transistoraccording to the first embodiment of the present invention. Here, thelow voltage drive transistors are ultra-high threshold NMOS transistorswhere the gate width W is 10 μm, the gate length L is 0.14 μm, and thedrive voltage is 1.2 V, and the results of the measurements are gainedfrom plots of 71 NMOS transistors, from which it can be seen that theinconsistency is small in the case of the first embodiment of thepresent invention. This is considered to be because CoSi spikes aresuppressed.

FIG. 18 is a graph illustrating the median values of the leak currentsfrom n channel type MOS transistors, and illustrates the median valuesof the results of the measurements in FIGS. 17A and 17B. Here, themedian values of the LVI/OTr that has a ballast resistor and a typicalLVTr that does not have a ballast resistor according to the firstembodiment of the present invention are illustrated. As can be clearlyseen from the figures, the leak current is reduced in the firstembodiment of the present invention.

FIGS. 19A and 19B are diagrams illustrating the results of simulation ofthe distribution of the impurity concentration in the n channel type lowvoltage drive transistor with a ballast resistor according to the firstembodiment of the present invention, and illustrate the distribution ofthe impurity concentration in the vicinity of the ballast resistor. FIG.19A illustrates the distribution of the impurity concentration in atypical LVI/OTr to be compared, and FIG. 19B illustrates thedistribution of the impurity concentration in the LVI/OTr according tothe first embodiment of the present invention. As can be clearly seenfrom the figures, the junction position is deeper and the impurityconcentration is lower in the first embodiment of the present invention.

FIG. 20 is a graph illustrating the distribution of the effectiveimpurity concentration, and illustrates the profile of the effectiveimpurity concentration in the ballast resistor portion in FIGS. 19A and19B. As illustrated in the figure, the pn junction in the typicalLVI/OTr is located approximately 0.02 μm from the surface while the pnjunction in the LVI/OTr according to the first embodiment of the presentinvention is located approximately 0.24 μm from the surface. Inaddition, the effective impurity concentration is 1×10¹⁸ cm⁻³ or lower.Accordingly, band-to-band tunneling (BTBT) can be suppressed due to thelow impurity concentration.

FIGS. 21A, 21B, and 22 are graphs illustrating the characteristics of ap channel type low voltage drive transistor to which the structureaccording to the first embodiment of the present invention is applied.FIGS. 21A and 21B are graphs illustrating the results of themeasurements of a leak current from a p channel type MOS transistor.FIG. 21A is a characteristic graph of a typical transistor to becompared, and FIG. 21B is a characteristic graph of the transistoraccording to the first embodiment of the present invention. Here aswell, the low voltage drive transistors are ultra-high threshold PMOStransistors where the gate width W is 10 μm, the gate length L is 0.14μm, and the drive voltage is 1.2 V, and the results of the measurementsare gained from plots of 71 NMOS transistors.

FIG. 22 is a graph illustrating the median value of the leak currentfrom a p channel type MOS transistor, and illustrates the median valueof the results of the measurements in FIGS. 21A and 21B. Here, themedian values of the LVI/OTr that has a ballast resistor and a typicalLVTr that does not have a ballast resistor according to the firstembodiment of the present invention are illustrated. As can be clearlyseen from the figures, the leak current is reduced in the firstembodiment of the present invention.

FIGS. 23A and 23B are diagrams illustrating the results of simulation ofthe distribution of the impurity concentration in the p channel type lowvoltage drive transistor with a ballast resistor according to the firstembodiment of the present invention, and illustrates the distribution ofthe impurity concentration in the vicinity of the ballast resistor. FIG.23A illustrates the distribution of the impurity concentration of atypical LVI/OTr to be compared, and FIG. 23B illustrates thedistribution of the impurity concentration of the LVI/OTr according tothe first embodiment of the present invention. As can be clearly seenfrom the figures, the junction position is deeper and the impurityconcentration is lower in the first embodiment of the present invention.

FIG. 24 is a graph illustrating the distribution of the effectiveimpurity concentration, and illustrates the profile of the effectiveimpurity concentration in the ballast resistor portion in FIGS. 23A and23B. As illustrated in the figure, the pn junction in the typicalLVI/OTr is located approximately 0.02 μm from the surface while the pnjunction in the LVI/OTr according to the first embodiment of the presentinvention is located approximately 0.36 μm from the surface. Inaddition, the effective impurity concentration is 1×10¹⁸ cm⁻³ or lower.Accordingly, band-to-band tunneling (BTBT) can be suppressed due to thelow impurity concentration.

In the first embodiment of the present invention, the ballast resistoris formed in the process for forming LDD regions in a high voltage drivetransistor, and therefore, the pn junction can be located deeper andmade with a lower impurity concentration, and as a result, it ispossible to reduce the leak current that occurs together with BTBT andlower the inconsistency.

Second Embodiment

Next, the semiconductor integrated circuit apparatus according to thesecond embodiment of the present invention is described in reference toFIGS. 25 to 26J. FIG. 25 is a schematic cross-sectional diagramillustrating the semiconductor integrated circuit apparatus according tothe second embodiment of the present invention where flash memory cellsare added to the semiconductor integrated circuit apparatus according tothe first embodiment. Though FIG. 25 illustrates the transistors thatform a peripheral circuit, an internal logic circuit, and an I/O unit,and a flash memory cell portion at two separate levels in order to makethe illustrating easy to understand, they are actually formed on thesame substrate.

The transistors that form a peripheral circuit, an internal logiccircuit, and an I/O unit are exactly the same as in the firstembodiment, and therefore, the flash memory cell portion is describedbelow. A flash memory element is provided with a gate electrode portionmade of a tunnel oxide film 88, a floating gate 92, an ONO film 90, anda control gate 93, and with side walls 75 and 96 with a three-layerstructure of an oxide film (not shown), an SiN film, and an oxide film.

Next, the manufacturing process for the flash memory cell portion isdescribed in reference to FIGS. 26A to 26J. First, as illustrated inFIG. 26A, a p type well region 85 is formed within the same process fora high voltage drive transistor (HVTr) during the process for formingrespective wells for the transistors that form the peripheral circuit,the internal logic circuit, and the I/O unit. Then, a resist pattern 86is used as a mask to implant B ions, and thus, a p type channel doperegion 87 is formed.

Next, as illustrated in FIG. 26B, the sacrificial oxide film made of aSiO₂ film 53 is removed and a tunnel oxide film 88, of which thethickness is 10 nm, for example, is formed on the surface of the p typewell region 85 through thermal oxidation before the formation of gateoxide films in other regions.

Next, as illustrated in FIG. 26C, an amorphous silicon layer 89, ofwhich the thickness is 70 nm, for example, and into which P is doped, isformed and then etched so as to remain only on the p type well region85. After that, a SiO₂ film, of which the thickness is 5 nm, forexample, and an SiN film, of which the thickness is 10 nm, for example,are deposited on the entire surface, which is then followed by thermaloxidation at 950° C. for 90 minutes, for example, so as to gain an ONOfilm 90, of which the total thickness is approximately 20 nm, forexample. Then, as illustrated in FIG. 26D, the resist pattern 91 is usedas a mask for etching so as to remove the ONO film 90 that has beendeposited on the areas other than the p type well region 85.

Next, as illustrated in FIG. 26E, gate electrode portions made of atunnel oxide film 88, a floating gate 92, an ONO film 90, a control gate93, and an SiN film 94 are formed before processing the polycrystallinesilicon layer that has been deposited on other regions into gateelectrodes.

Next, as illustrated in FIG. 26F, the gate electrode portions are usedas a mask so that As ions are implanted at a tilt angle of 0° with anacceleration energy of 50 keV so as to gain an amount of dosage of6.0×10¹⁴ cm⁻², for example, and thus, n type LDD regions 95 are formed.

Next, as illustrated in FIG. 26G, thin oxide films (not shown) areformed on the sides of the gate electrode portions through thermaloxidation, and after that, an SiN film is deposited on the entiresurface, which is then followed by anisotropic etching so that sidewalls 96 made of the SiN film are formed. After this process, thepolycrystalline silicon layer that has been deposited on other regionsis etched so as to form gate electrodes (65 to 67).

Next, as illustrated in FIG. 26H, side walls 75 are formed of a SiO₂film on the sides of the gate electrode structures of flash memoryelements during the process for forming side walls 75 on the sides ofthe gate electrodes that have been formed in other regions.

Next, as illustrated in FIG. 26I, the side walls 75 and 96 are used as amask to implant P ions so that n+type source/drain regions 97 are formedduring the process for forming sources/drains in other regions.

Next, as illustrated in FIG. 26J, a Co silicide layer 84 is formed onthe surfaces of the n+type source/drain regions 97 and the control gates93 during the process for forming a Co silicide layer 84 on the surfacesof the source/drain regions and the gate electrodes in other regions.After that, though not shown, an interlayer insulating film is formed,and then, plugs that reach a Co silicide layer 84 are formed, which isfollowed by the formation of wires connected to these plugs. Theformation of such a wire structure is repeated for the required numberof layers, and thus, the basic structure of the semiconductor integratedcircuit apparatus according to the second embodiment of the presentinvention is complete.

In the semiconductor integrated circuit apparatus with flash memoryelements according to the second embodiment of the present invention aswell, the ballast resistor in the LVI/OTr is formed during the LDDforming process for the HVTr, and therefore, the leak current can bereduced and the inconsistency in the sheet resistance can also bereduced.

Third Embodiment

Next, the semiconductor integrated circuit apparatus according to thethird embodiment of the present invention is described in reference toFIGS. 27A to 29B. First, the manufacturing method for the semiconductorintegrated circuit apparatus according to the third embodiment of thepresent invention is described in reference to FIGS. 27A to 27J. Asillustrated in FIG. 27A, in the same manner as in the first embodiment,an element isolation region 52 is formed on a silicon substrate 51 bymeans of STI, and then, a p type well region 55 of 2.2×10¹⁷ cm⁻³, forexample, is formed in the high voltage drive Tr forming region. Afterthat, p type well regions 57 and 58 of 9.6×10¹⁷ cm⁻³, for example, areformed in low voltage drive Tr forming regions. Then, the resist pattern59 is used as a mask to form p type channel dope regions 60 and 61 onthe surface of a portion of the p type well region 57 and the p typewell region 58. After that, as illustrated in FIG. 27B, a SiO₂ film 62,of which the thickness is 16 nm, for example, that becomes a gateinsulating film of a high voltage drive Tr is formed through thermaloxidation.

Next, as illustrated in FIG. 27C, a resist pattern 63 is formed so as tocover the p type well region 55 and a portion of the p type well region57, and then, the SiO₂ film 62 on the exposed p type well regions 57 and58 is removed through etching.

Next, as illustrated in FIG. 27D, the resist pattern 63 is removed,which is then followed by thermal oxidation again so that a SiO₂ film64, of which the thickness is 1.8 nm, for example, that becomes a gateinsulating film of a low voltage drive Tr is formed on the surface ofthe p type well regions 57 and 58.

Next, as illustrated in FIG. 27E, a polycrystalline silicon layer isdeposited on the p type well regions 55, 57, and 58, which is thenfollowed by etching so that gate electrodes 65 to 67 are formed. At thistime, the film thickness of the SiO₂ film 62 on the ballast formingregion is reduced by approximately 5 nm during the gate etching process,and at the same time, the thin SiO₂ films 64 that have been exposedessentially disappear.

Next, as illustrated in FIG. 27F, a resist pattern 68 is formed so as tocover the region in the p type well region 57 where the p type channeldope region 60 is formed and the p type well region 58. After that, thisresist pattern 68 is used as a mask so as to implant P ions in fourdirections at a tilt angle of 45° with an acceleration energy of 46 keV,for example, so that an amount of dosage becomes 8.0×10¹² cm⁻², andthus, n type LDD regions 69 are formed in the p type well region 55, andat the same time, an n−type region 70 is formed in the exposed portionof the p type well region 57. At this time, the SiO₂ film 62 is providedon the n−type region 70, and therefore, the channeling factor issuppressed and the inconsistency due to the tilt angle is reduced, andthus, a stable sheet resistance value can be gained.

Next, as illustrated in FIG. 27G, the resist pattern 68 is removed, andthen, a new resist pattern 71 is formed so as to cover the p type wellregion 55 and the n−type region 70. This resist pattern 71 is used as amask so as to implant B ions in four directions at a tilt angle of 28°with an acceleration energy of 15 keV, for example, so that the amountof dosage becomes 7.4×10¹² cm⁻², for example, and thus, pocket regions(not shown) are formed. Subsequently, P ions are implanted in fourdirections at a tilt angle of 0° with an acceleration energy of 1 keV,for example, so that the amount of dosage becomes 6.0×10¹³ cm⁻², and Asions are implanted in four directions at a tilt angle of 0° with anacceleration energy of 1 keV, for example, so that the amount of dosagebecomes 1.0×10¹⁴ cm⁻², for example, and thus, n type extension regions72 and 73 are formed in the p type well regions 57 and 58.

Next, as illustrated in FIG. 27H, the resist pattern 71 is removed, andthen, a SiO₂ film is deposited on the entire surface. After that, aresist pattern 74 is formed so as to cover the ballast resistor formingregion, which is then followed by anisotropic etching so that side walls75 are formed. At this time, the SiO₂ film that remains beneath theresist pattern 74 becomes a salicide block 76.

Next, as illustrated in FIG. 27I, the resist pattern 74 is removed, andthen, P ions are implanted at a tilt angle of 0° with an accelerationenergy of 8 keV, for example, so that the amount of dosage becomes1.2×10¹⁶ cm⁻², and thus, n+type source regions 77, 79, and 81 as well asn+type drain regions 78, 80, and 82 are formed. At this time, the n−typeregion directly beneath the salicide block 76 becomes a ballast resistor83.

Next, as illustrated in FIG. 27J, a Co film is deposited on the entiresurface, which is then followed by heat treatment so that a Co silicidelayer 84 is formed on the surface of the gate electrodes 65 to 67, then+type source regions 77, 79, and 81 as well as the n+type drain regions78, 80, and 82. After that, the unreacted portions of the Co film areremoved, which is then followed by heat treatment again so that theresistance of the Co silicide layer 84 is lowered. After that, thoughnot shown, an interlayer insulating film is formed, and then, plugs thatreach a Co silicide layer 84 are formed, which is followed by theformation of wires connected to these plugs. The formation of such awire structure is repeated for the required number of layers, and thus,the basic structure of the semiconductor integrated circuit apparatusaccording to the third embodiment of the present invention is complete.

FIGS. 28A and 28B illustrate profiles of the impurity concentrations inthe ballast resistor portion of an NMOS. FIG. 28A illustrates profilesof the impurity concentrations in the ballast resistor portion of theLVI/OTr according to the third embodiment of the present invention, andFIG. 28B illustrates profiles of the impurity concentrations in theballast resistor portion of the LVI/OTr according to the firstembodiment to be compared. As is clear from FIG. 28A, almost no changeis observed in the profiles when the tilt angle is varied between 42°and 48° in the case where the thickness of the SiO₂ film 62 is 11 nm.Meanwhile, as illustrated in FIG. 28B, inconsistency is observed in theprofiles in the case where the thickness of the SiO₂ film 62 is 0 nm.

As can be clearly seen from the comparison between FIGS. 28A and 28B,the channeling factor is reduced, and thus, the inconsistency in theprofiles due to the tilt angle is reduced by providing a SiO₂ film whenan n type low impurity concentration layer is formed for the ballastresistor.

FIGS. 29A and 29B illustrate profiles of the impurity concentrations inthe ballast resistor portion of a PMOS. FIG. 29A illustrates profiles ofthe impurity concentrations in the ballast resistor portion of the pchannel type LVI/OTr, to which the second embodiment of the presentinvention is applied. FIG. 29B illustrates profiles of the impurityconcentrations in the ballast resistor portion of the p channel typeLVI/OTr, to which the first embodiment is applied for comparison. As isclear from FIG. 29A, almost no change is observed in the profiles whenthe tilt angle is varied between 42° and 48° in the case where thethickness of the SiO₂ film 62 is 11 nm. Meanwhile, as illustrated inFIG. 29B, inconsistency is observed in the profiles in the case wherethe thickness of the SiO₂ film 62 is 0 nm.

As can be clearly seen from the comparison between FIGS. 29A and 29B,the channeling factor is reduced, and thus, the inconsistency in theprofiles due to the tilt angle is reduced by providing a SiO₂ film whena p type low impurity concentration layer is formed for the ballastresistor.

In the third embodiment of the present invention as well, the ballastresistor is formed in the process for forming LDD regions in a highvoltage drive transistor, and therefore, the pn junction can be locateddeeper and made with a lower impurity concentration, and as a result, itis possible to reduce the leak current that occurs together with BTBTand lower the inconsistency. In addition, ions are implanted through aSiO₂ film for the formation of a ballast resistor during the process forforming the LDD regions in a high voltage drive transistor, andtherefore, the channeling factor can be reduced and the inconsistency inthe profiles due to the tilt angle can also be reduced.

Fourth Embodiment

Next, the semiconductor integrated circuit apparatus according to thefourth embodiment of the present invention is described in reference toFIGS. 30A to 30J. First, as illustrated in FIG. 30A, in the same manneras in the first embodiment, an element isolation region 52 is formed ona silicon substrate 51 by means of STI, and then, a p type well region55 of 2.2×10¹⁷ cm⁻³, for example, is formed in the high voltage drive Trforming region. After that, p type well regions 57 and 58 of 9.6×10¹⁷cm⁻³, for example, are formed in low voltage drive Tr forming regions.

Next, p type channel dope regions 60 and 61 are formed on the surface ofa portion of the p type well region 57 and the p type well region 58.After that, a SiO₂ film 62, of which the thickness is 16 nm, forexample, that becomes a gate insulating film of a high voltage drive Tris formed through thermal oxidation.

Next, as illustrated in FIG. 30B, a resist pattern 63 is formed so as tocover the p type well region 55, and then, the SiO₂ film 62 on theexposed p type well regions 57 and 58 is removed through etching.

Next, as illustrated in FIG. 30C, the resist pattern 63 is removed,which is then followed by thermal oxidation again so that a SiO₂ film64, of which the thickness is 1.8 nm, for example, that becomes a gateinsulating film of a low voltage drive Tr is formed on the surface ofthe p type well regions 57 and 58. Next, as illustrated in FIG. 30D, apolycrystalline silicon layer is deposited on the p type well regions55, 57, and 58, and then etched so that gate electrodes 65 to 67 areformed.

Next, as illustrated in FIG. 30E, a new resist pattern 71 is formed soas to cover the p type well region 55 and the region in the p type wellregion 57 where the p type channel dope region 60 is not formed. Thisresist pattern 71 is used as a mask so as to implant B ions in fourdirections at a tilt angle of 0° with an acceleration energy of 15 keV,for example, so that the amount of dosage becomes 7.4×10¹² cm⁻², forexample, and thus, pocket regions (not shown) are formed. Subsequently,P ions are implanted in four directions at a tilt angle of 0° with anacceleration energy of 1 keV, for example, so that the amount of dosagebecomes 6.0×10¹³ cm⁻², and As ions are implanted in four directions at atilt angle of 0° with an acceleration energy of 1 keV, for example, sothat the amount of dosage becomes 1.0×10¹⁴ cm⁻², for example, and thus,n type extension regions 72 and 73 are formed in the p type well regions57 and 58.

Next, as illustrated in FIG. 30F, the resist pattern 71 is removed, andthen, a SiO₂ film 98, of which the thickness is 3 nm, for example, isdeposited on the entire surface in accordance with a CVD method.

Next, as illustrated in FIG. 30G, a resist pattern 68 is formed so as tocover the region in the p type well region 57 where the p type channeldope region 60 is formed and the p type well region 58. After that, thisresist pattern 68 is used as a mask so as to implant P ions in fourdirections at a tilt angle of 45° with an acceleration energy of 46 keV,for example, so that an amount of dosage becomes 8.0×10¹² cm⁻², andthus, n type LDD regions 69 are formed in the p type well region 55, andat the same time, an n−type region 70 is formed in the exposed portionof the p type well region 57. At this time, the SiO₂ film 98 is providedon the n−type region 70, and therefore, the channeling factor issuppressed and the inconsistency due to the tilt angle is reduced, andthus, a stable sheet resistance value can be gained.

Next, as illustrated in FIG. 30H, the resist pattern 68 is removed, andthen, a SiO₂ film is deposited on the entire surface. After that, aresist pattern 74 is formed so as to cover the ballast resistor formingregion, which is then followed by anisotropic etching so that side walls75 are formed. At this time, the SiO₂ film that remains beneath theresist pattern 74 becomes a salicide block 76.

Next, as illustrated in FIG. 301, the resist pattern 74 is removed, andthen, P ions are implanted at a tilt angle of 0° with an accelerationenergy of 8 keV, for example, so that the amount of dosage becomes1.2×10¹⁶ cm⁻², and thus, n+type source regions 77, 79, and 81 as well asn+type drain regions 78, 80, and 82 are formed. At this time, the n−typeregion directly beneath the salicide block 76 becomes a ballast resistor83.

Next, as illustrated in FIG. 30J, a Co film is deposited on the entiresurface, which is then followed by heat treatment so that a Co silicidelayer 84 is formed on the surface of the gate electrodes 65 to 67, then+type source regions 77, 79, and 81 as well as the n+type drain regions78, 80, and 82. After that, the unreacted portions of the Co film areremoved, which is then followed by heat treatment again so that theresistance of the Co silicide layer 84 is lowered. After that, thoughnot shown, an interlayer insulating film is formed, and then, plugs thatreach a Co silicide layer 84 are formed, which is followed by theformation of wires connected to these plugs. The formation of such awire structure is repeated for the required number of layers, and thus,the basic structure of the semiconductor integrated circuit apparatusaccording to the fourth embodiment of the present invention is complete.

In the fourth embodiment of the present invention as well, in the samemanner as in the third embodiment ions are implanted through a SiO₂ filmfor the formation of a ballast resistor during the process for formingthe LDD regions in a high voltage drive transistor, and therefore, thechanneling factor is reduced. As a result, the inconsistency in theprofiles due to the tilt angle can be reduced.

Fifth Embodiment

Next, the complementary type semiconductor integrated circuit apparatusaccording to the fifth embodiment of the present invention is describedin reference to FIGS. 31A to 31L. First, as illustrated in FIG. 31A, anelement isolation region 102 is formed in a silicon substrate 101 bymeans of STI, and then, a SiO₂ film 103, of which the thickness is 10nm, for example, that becomes a sacrificial oxide film is formed on thesurface. After that, an n type low voltage drive Tr forming region iscovered with a resist pattern 104 and ion implanted with P so that ntype well regions 105 and 106 of 7.8×10¹⁷ cm⁻³, for example, are formed.

Next, as illustrated in FIG. 31B, the resist pattern 104 is removed, andthen, a p type low voltage drive Tr forming region is covered with aresist pattern 107 and ion implanted with B so that p type well regions108 and 109 of 9.6×10¹⁷ cm⁻³, for example, are formed.

Next, as illustrated in FIG. 31C, the resist pattern 107 is removed, andthen, a resist pattern 110 is provided so as to cover a portion of the ptype well region 108, a portion of the n type well region 105, and theentirety of the n type well region 106. After that, the resist pattern110 is used as a mask to implant B ions at a tilt angle of 7° with anacceleration energy of 15 keV, for example, so that the amount of dosagebecomes 6.5×10¹² cm⁻² to 1.9×10¹³ cm⁻², for example, and thus, p typechannel dope regions 111 and 112 are formed in the exposed portions ofthe p type well regions 108 and 109. At this time, a p−type region 113is simultaneously formed in the exposed portion of the n type wellregion 105.

Next, as illustrated in FIG. 31D, the resist pattern 110 is removed, andthen, a resist pattern 114 is provided so as to cover a portion of the ptype well region 108, the entirety of the p type well region 109, and aportion of the n type well region 105. After that, the resist pattern114 is used as a mask to implant P ions at a tilt angle of 7° with anacceleration energy of 65 keV, for example, so that the amount of dosagebecomes 8.0×10¹² cm⁻² to 3.0×10¹³ cm⁻², for example, and thus, n typechannel dope regions 115 and 116 are formed in the exposed portions ofthe n type well regions 105 and 106. At this time, an n−type region 117is simultaneously formed in the exposed portion of the p type wellregion 108.

Next, as illustrated in FIG. 31E, the resist pattern 114 is removed, andthen, the SiO₂ film 103 is removed, which is then followed by thermaloxidation so that a SiO₂ film 118, of which the thickness is 1.8 nm, forexample, that becomes a gate insulating film is formed. After that, asillustrated in FIG. 31F, a polycrystalline silicon layer is deposited onthe p type well regions 108 and 109 as well as the n type well regions105 and 106, and then etched so as to form gate electrodes 119 to 122.

Next, as illustrated in FIG. 31G, a resist pattern 123 is formed so asto cover the n−type region 117 and the n type well regions 105 and 106.After that, this resist pattern 123 is used as a mask to implant B ionsin four directions at a tilt angle of 28° with an acceleration energy of15 keV, for example, so that the amount of dosage becomes 7.4×10¹² cm⁻²,for example, and thus, pocket regions (not shown) are formed.Subsequently, P ions are implanted in four directions at a tilt angle of0° with an acceleration energy of 1 keV, for example, so that the amountof dosage becomes 6.0×10¹³ cm⁻², and As ions are implanted in fourdirections at a tilt angle of 0° with an acceleration energy of 1 keV,for example, so that the amount of dosage becomes 1.0×10¹⁴ cm⁻², forexample, and thus, n type extension regions 124 and 125 are formed inthe p type well regions 108 and 109.

Next, as illustrated in FIG. 31H, a resist pattern 126 is formed so asto cover the p type well regions 108 and 109 as well as the p−typeregion 113. After that, this resist pattern 126 is used as a mask toimplant P ions in four directions at a tilt angle of 28° with anacceleration energy of 40 keV, for example, so that the amount of dosagebecomes 7.4×10¹² cm⁻², for example, and thus, pocket regions (not shown)are formed. Subsequently, B ions are implanted in four directions at atilt angle of 0° with an acceleration energy of 0.3 keV, for example, sothat the amount of dosage becomes 7.8×10¹³ cm⁻², for example, and thus,p type extension regions 127 and 128 are formed in the n type wellregions 105 and 106.

Next, as illustrated in FIG. 311, the resist pattern 126 is removed, andthen, a SiO₂ film is deposited on the entire surface. After that, aresist pattern 129 is formed so as to cover the ballast resistor formingregion, which is then followed by anisotropic etching so that side walls130 are formed. At this time, the SiO₂ film that remains beneath theresist pattern 129 becomes salicide blocks 131 and 132.

Next, as illustrated in FIG. 31J, the resist pattern 129 is removed, andthen, a resist pattern 133 is formed so as to cover the n type wellregions 105 and 106. After that, the resist pattern 133 is used as amask to implant P ions at a tilt angle of 0° with an acceleration energyof 8 keV, for example, so that the amount of dosage becomes 2×10¹⁶ cm⁻²,for example, and thus, n+type source regions 134 and 136 as well asn+type drain regions 135 and 137 are formed. At this time, the n−typeregion directly beneath the salicide block 131 becomes a ballastresistor 138.

Next, as illustrated in FIG. 31K, the resist pattern 133 is removed, andthen, a resist pattern 139 is formed so as to cover the p type wellregions 108 and 109. After that, the resist pattern 139 is used as amask to implant B ions at a tilt angle of 0° with an acceleration energyof 4 keV, for example, so that the amount of dosage becomes 6.0×10¹⁵cm⁻², for example, and thus, p+type source regions 140 and 142 as wellas p+type drain regions 141 and 143 are formed. At this time, the p−typeregion directly beneath the salicide block 132 becomes a ballastresistor 144.

Next, as illustrated in FIG. 31L, a Co film is deposited on the entiresurface, which is then followed by heat treatment so that a Co silicidelayer 145 is formed on the surface of the gate electrodes 119 to 122,the n+type source regions 134 and 136, the n+type drain regions 135 and137, and the p type source regions 140 and 142 as well as the p+typedrain regions 141 and 143. After that, the unreacted portions of the Cofilm are removed, which is then followed by heat treatment again so thatthe resistance of the Co silicide layer 145 is lowered. After that,though not shown, an interlayer insulating film is formed, and then,plugs that reach a Co silicide layer 145 are formed, which is followedby the formation of wires connected to these plugs. The formation ofsuch a wire structure is repeated for the required number of layers, andthus, the basic structure of the complementary type semiconductorintegrated circuit apparatus according to the fifth embodiment of thepresent invention is complete.

Here, the dispersion of the impurity concentration and the leak currentin the ballast resistors are simulated, and therefore, the results ofthe examination are described in reference to FIGS. 32A to 40B. FIGS.32A to 32C are diagrams illustrating the dependency of the distributionof the impurity concentration in an n type ballast resistor region. FIG.32A is a diagram illustrating the distribution of the impurityconcentration in an UHVth, FIG. 32B is a diagram illustrating thedistribution of the impurity concentration in a HVth, and FIG. 32C is adiagram illustrating the distribution of the impurity concentration in aSVth. As illustrated in the figures, the UHVth with a large amount ofchannel dosage has a deep pn junction and a high impurity concentration.

FIGS. 33A to 33C are diagrams illustrating the dependency of thedistribution of the impurity concentration in a p type ballast resistorregion on the amount of channel dosage. FIG. 33A is a diagramillustrating the distribution of the impurity concentration in an UHVth,FIG. 33B is a diagram illustrating the distribution of the impurityconcentration in a HVth, and FIG. 33C is a diagram illustrating thedistribution of the impurity concentration in a SVth. As illustrated inthe figures, in the case of p type as well, the UHVth with a largeamount of channel dosage has a deep pn junction and a high impurityconcentration.

FIGS. 34A and 34B are graphs illustrating the results of evaluation ofthe leak current in ballast resistor regions. FIG. 34A is a graphillustrating the leak current in n channel type MOS transistors (NMOSs),and FIG. 34B is a graph illustrating the leak current in p channel typeMOS transistors (PMOSs). As is clear from the figures, no increase inthe leak current is observed in the same manner as in the LVTr in thefirst embodiment in either case of UHVth, HVth, or SVth.

FIGS. 35A and 35B are diagrams illustrating the results of simulation ofthe distribution of the impurity concentration in an n channel type lowvoltage drive transistor with a ballast resistor, which is the UHVthaccording to the fifth embodiment of the present invention, andillustrate the distribution of the impurity concentration in thevicinity of the ballast resistor. FIG. 35A illustrates the distributionof the impurity concentration in a typical LVI/OTr to be compared, andFIG. 35B illustrates the distribution of the impurity concentration inthe LVI/OTr according to the fifth embodiment of the present invention.As can be clearly seen from the figures, the junction is located deeperand the impurity concentration is lower in the fifth embodiment of thepresent invention.

FIG. 36 is a graph showing the distribution of the effective impurityconcentration, and illustrates profiles of the effective impurityconcentration in the ballast resistor portion in FIGS. 35A and 35B. Asillustrated in the figures, the pn junction is located at approximately0.02 μm from the surface in the typical LVI/OTr while the pn junction islocated at approximately 0.22 μm from the surface in the LVI/OTr in thefifth embodiment of the present invention. In addition, the effectiveimpurity concentration is approximately 1×10¹⁸ cm⁻³. Accordingly, theimpurity concentration is low and band-to-band tunneling (BTBT) can besuppressed.

FIGS. 37A and 37B are diagram illustrating the results of simulation ofthe distribution of the impurity concentration in a p channel type lowvoltage drive transistor with a ballast resistor, which is the UHVthaccording to the fifth embodiment of the present invention, andillustrate the distribution of the impurity concentration in thevicinity of the ballast resistor. FIG. 37A illustrates the distributionof the impurity concentration in a typical LVI/OTr to be compared, andFIG. 37B illustrates the distribution of the impurity concentration inthe LVI/OTr according to the fifth embodiment of the present invention.As can be clearly seen from the figures, the junction is located deeperand the impurity concentration is lower in the fifth embodiment of thepresent invention.

FIG. 38 is a graph showing the distribution of the effective impurityconcentration, and illustrates profiles of the effective impurityconcentration in the ballast resistor portion in FIGS. 37A and 37B. Asillustrated in the figures, the pn junction is located at approximately0.02 μm from the surface in the typical LVI/OTr while the pn junction islocated at approximately 0.17 μm from the surface in the LVI/OTr in thefifth embodiment of the present invention. In addition, the effectiveimpurity concentration is 1×10¹⁸ cm⁻³ or lower. Accordingly, theimpurity concentration is low and band-to-band tunneling (BTBT) can besuppressed.

FIGS. 39A and 39B are graphs illustrating the selectivity of the sheetresistance in an n channel type MOS transistor. FIG. 39A illustrates thevalues, for comparison, of the sheet resistance measured in the casewhere an LDD forming process is used for HVTr instead of channel doping.FIG. 39B illustrates the sheet resistance values gained from thesimulation in the case where the channel doping process according to thefifth embodiment of the present invention is used.

As is clear from the comparison between FIGS. 39A and 39B, one value isdetermined for the sheet resistance in the case of the LDD formingprocess while the sheet resistance can be changed between the samenumber of values as the channel doping steps for different VThs in thecase where a channel doping process is used. Accordingly, an optimalsheet resistance value can be selected from the evaluation values forthe ESD tolerance by using a channel doping process.

FIGS. 40A and 40B are graphs illustrating the sheet resistanceselectivity in a p channel type MOS transistor. FIG. 40A illustrates thevalues, for comparison, of the sheet resistance measured in the casewhere an LDD forming process is used for HVTr instead of channel doping.FIG. 40B illustrates the sheet resistance values gained from thesimulation in the case where the channel doping process according to thefifth embodiment of the present invention is used. Here, in the case ofa PMOS, there are two sets of sheet resistance values because Vth is setby varying the conditions for pocket injection and extension injectionfor an NMOS under the supposition that the channel doping conditions arethe same between HVth and SVth.

As is clear from the comparison between FIGS. 40A and 40B, in the caseof a PMOS as well, one value is determined for the sheet resistance inthe case of the LDD forming process while the sheet resistance can bechanged between the same number of values as the channel doping steps inthe case where a channel doping process is used. Accordingly, an optimalsheet resistance value can be selected from the evaluation values forthe ESD tolerance by using a channel doping process.

In the fifth embodiment of the present invention, the ballast resistoris formed by using a process for forming a channel dope region of atransistor of the opposite conductivity type, and therefore, the pnjunction can be located deep and be of a low impurity concentration, andat the same time, it is possible to select any sheet resistance value.As a result, it is possible to reduce the leak current that occurstogether with BTBT and reduce the inconsistency of the leak current, andat the same time, it is possible to increase the ESD tolerance.

All examples and conditional language provided herein are intended forthe pedagogical purposes of aiding the reader in understanding theinvention and the concepts contributed by the inventor to further theart, and are not to be construed as limitations to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although one or more embodiments of thepresent invention have been described in detail, it should be understoodthat the various changes, substitutions, and alterations could be madehereto without departing from the spirit and scope of the invention.

What is claimed is:
 1. A semiconductor integrated circuit apparatus,comprising a first insulated gate transistor that includes: a first wellregion of a first conductivity type in a semiconductor substrate; afirst gate electrode provide on the first well region with a first gateinsulating film in between; a first channel dope region of the firstconductivity type provided beneath the first gate electrode; a firstextension region of a second conductivity type that is a conductivitytype opposite to the first conductivity type, a first source region ofthe second conductivity type, and a first drain region of the secondconductivity type provided on both sides of the first gate electrode;and a first ballast resistor of the second conductivity type thatseparates the first drain region, wherein a peak impurity concentrationof the first ballast resistor is lower than a peak impurityconcentration of the first extension region, and a depth of the firstballast resistor is greater than a depth of the first extension region.2. The semiconductor integrated circuit apparatus according to claim 1,characterized by further including an insulating film pattern thatbecomes a salicide block directly above the first ballast resistor. 3.The semiconductor integrated circuit apparatus according to claim 1,further comprises a second insulated gate transistor of which a drivevoltage is higher than a drive voltage of the first insulated gatetransistor, that includes: a second well region of the firstconductivity type in the semiconductor substrate, a second gateelectrode provided in the second well region with a second gateinsulating film in between; a low concentration source/drain region ofthe second conductivity type, a second source region of the secondconductivity type of which an impurity concentration is higher than animpurity concentration of the low concentration source/drain region, anda second drain region of the second conductivity type of which animpurity concentration is higher than the impurity concentration of thelow concentration source/drain region provided on both sides of thesecond gate electrode, characterized in that an impurity concentrationof the first ballast resistor is the same or higher than the impurityconcentration of the low concentration source/drain region, and thedepth of the first ballast resistor is the same or greater than a depthof the low concentration source/drain region.
 4. The semiconductorintegrated circuit apparatus according to claim 1, further comprises athird insulated gate transistor of which a drive voltage is the same asthe drive voltage of the first insulated gate transistor, that includes:a third well region of the first conductivity type in the semiconductorsubstrate, a third gate electrode provided in the third well region witha third gate insulating film in between; a second channel dope region ofthe first conductivity type provided beneath the third gate electrode;and a second extension region of the second conductivity type, a thirdsource region of the second conductivity type, and a third drain regionof the second conductivity type provided on the two sides of the thirdgate electrode.
 5. The semiconductor integrated circuit apparatusaccording to claim 1 , further includes a number of flash memoryelements with a floating gate in a fourth well region of the firstconductivity type in the semiconductor substrate.
 6. The semiconductorintegrated circuit apparatus according to claim 1, further includes afourth insulated gate transistor that comprises: a fourth well region ofthe second conductivity type in the semiconductor substrate, a fourthgate electrode provided in the first well region of the secondconductivity type with a fourth gate insulating film in between; a thirdchannel dope region of the second conductivity type provided beneath thefourth gate electrode; a third extension region of the firstconductivity type, a fourth source region of the first conductivitytype, and a fourth drain region of the first conductivity type providedon the two sides of the fourth gate electrode; and a second ballastresistor of the first conductivity type that separates the fourth drainregion of the first conductivity type, the impurity concentration of thesecond conductivity type of the first ballast resistor has the samevalue gained by subtracting the value of the impurity concentration ofthe second conductivity type in the first well region of the secondconductivity type from the value of the impurity concentration of thesecond conductivity type in the third channel dope region, the depth ofthe first ballast resistor is the same as the depth of the third channeldope region, the impurity concentration of the first conductivity typeof the second ballast resistor has the same value gained by subtractingthe value of the impurity concentration of the first conductivity typein the first well region of the first conductivity type from the valueof the impurity concentration of the first conductivity type in thefirst channel dope region, and the depth of the second ballast resistoris the same as the depth of the first channel dope region.
 7. Asemiconductor integrated circuit apparatus, comprising a first insulatedgate transistor that includes: a first well region of a firstconductivity type in a semiconductor substrate; a first gate electrodeprovided on the first well region with a first gate insulating film inbetween; a first channel dope region of the first conductivity typeprovided beneath the first gate electrode; a first extension region of asecond conductivity type that is a conductivity type opposite to thefirst conductivity type, a first source region of the secondconductivity type, and a first drain region of the second conductivitytype provided on both sides of the first gate electrode; and a firstballast resistor of the second conductivity type that separates thefirst drain region, wherein a peak impurity concentration of the firstballast resistor is lower than a peak impurity concentration of thefirst extension region, and a depth of the first ballast resistor isgreater than a depth of the first extension region, and wherein adifference between the peak impurity concentration of the first ballastresistor and a peak impurity concentration of the first well region islower than a difference between the peak impurity concentration of thefirst extension region and a peak impurity concentration of the firstchannel dope region.